1. Field of the Invention
This invention relates to a packaging bag for photosensitive materials, particularly photographic photosensitive materials.
2. Description of the Prior Art
With respect to photosensitive materials which loses the qualitative values by exposing them to light, known packaging bags can shield light completely. It is necessary that packaging bags have sufficient physical strength, such as tensile strength, tear strength and bursting strength, according to the size and the weight of the packaged materials, and have excellent heat sealing properties because the opening of the bag is heat-sealed. It is also necessary to have antistatic properties in order to prevent static electrification caused by the friction between the photosensitive material and the bag.
Heretofore, the laminated films shown in FIG. 10 and FIG. 11 were used for such packaging bags. The laminated film of FIG. 10 is composed of a light shielding low density polyethylene (LDPE) resin layer 7a containing a light-shielding material, a metal foil layer 5 and a flexible sheet layer 6 laminated in this order each through an adhesive layer 4. The laminated film of FIG. 11 is composed of a laminated film having the same layer composition as FIG. 10 and another light-shielding LDPE resin layer 7a laminated on the flexible sheet layer 6 side through an adhesive layer 4. Besides, the inventor has already developed a packaging bag for photosensitive materials using a composite laminated film composed of a cross-laminated film, where two uniaxially stretched high density polyethylene resin films laminated to each other so that their stretched directions cross at an angle of 45 to 90 degrees, and a LDPE film laminated thereon (U.S. Pat. No. 4,147,291). The inventor has also developed another packaging material for photosensitive materials using a composite laminated sheet where two or more layers of uniaxially stretched high density polyethylene resin films having a draw ratio of 2 to 4.2 times are laminated so that their stretching axes cross at an angle of 45 to 90 degrees (U.S. Pat. No. 4,258,848).
However, the conventional composite laminated films composed of LDPE resin film(s), paper, aluminum foil, cellophane and the like are inferior in physical strength, and therefore, they were made thick. As a result, they are stiff, and the packages using them are bulky, heavy and expensive. In the above composite laminated films proposed by the inventor, physical strength and light-shielding ability are improved, and the packaging material using them can be made thinner, lighter and cheaper. However, at present, it is desired to develop an improved packaging material for photosensitive materials.